A conventionally known ultrasound probe is one in which a piezoelectric device, one or more acoustic matching layers, a first signal flexible board, a second signal flexible board, and a backing member are stacked on top of one another (e.g., see the following Patent Document 1).
FIG. 13 shows a cross-sectional perspective view of an ultrasound element portion (acoustic stack) 101 of an array scanning type ultrasound probe. The ultrasound element portion 101 includes the piezoelectric device 102 which is an electroacoustic conversion device made of PZT piezoelectric ceramic or the like, one or more acoustic matching layers 103, a first signal flexible board 104 which transfers electric signals to be transmitted to and received from the piezoelectric device 102, a second signal flexible board 105 which deals with electric signals of polarity opposite to that of the first signal flexible board 104, and a backing member 106 attached to the opposite side of the piezoelectric device 102 from the ultrasound emitting surface. The array scanning type ultrasound probe includes the ultrasound element portion 101, a housing (not shown) which covers the ultrasound element portion 101, a cable (not shown) for connection to an ultrasound diagnostic equipment (not shown), and the like.
In the ultrasound element portion 101, drive signals from the ultrasound diagnostic equipment (not shown) are applied to the piezoelectric device 102 through the first signal flexible board 104 and the second signal flexible board 105, converted into ultrasound signals by the piezoelectric device 102, and then applied to a subject (not shown) through the acoustic matching layers 103. Moreover, ultrasound signals reflected from the subject passes through the acoustic matching layers 103, and then are received and converted into electric signals by the piezoelectric device 102. The electric signals are sent to the ultrasound diagnostic equipment through the first signal flexible board 104 and the second signal flexible board 105 to undergo signal processing.
An ultrasound beam of the array scanning type ultrasound probe directed in the array (arrangement) direction (direction AA in the drawing) is formed into a desired beam shape to form a focal point at a predetermined depth, by controlling with the ultrasound diagnostic equipment several tens to several hundreds of individual elements 101a of the ultrasound element portion 101 which are divided in the array direction. Meanwhile, as to a direction (direction BB in the drawing, also expressed as the short axis direction) perpendicular to the array direction, an acoustic lens (not shown) which is generally made of silicone rubber or the like is used to form a focal point. This acoustic lens made of silicone rubber has frequency-dependent attenuation, and therefore deteriorates its sensitivity characteristics particularly when used in an array scanning type ultrasound probe using high frequencies. To address this, an array type ultrasound probe is known in which a flat piezoelectric device 102 is partly provided with incisions (kerfs) 107, and is mechanically curved with a certain curvature in the direction perpendicular to the array direction, thereby forming a focal point with the curvature instead of forming a beam shape by an acoustic lens.    Patent Document 1: Japanese Patent Application Publication H11-317999 (FIG. 1)
In the ultrasound element portion of the above-described conventional array scanning type ultrasound probe, the flat piezoelectric device 102 is partly provided with the incisions 107 and is mechanically curved with a certain curvature in the direction perpendicular to the array direction, thereby forming a focal point with the curvature. However, when mechanically curved, the piezoelectric device 102 made of ceramic or the like is apt to be cracked and damaged because stress concentrates at the regions of the incisions 107 of the piezoelectric device 102. This raises a problem that the damage reduces ultrasound of the array scanning type ultrasound probe at the time of transmission and reception, causing a sensitivity deterioration of a diagnostic image.